1. Field of the Invention
This invention relates to a process for preparing polyphenylene sulfide resins improved in regard to their well-known disadvantageous brittleness properties.
Because of their excellent heat resistance and chemical resistance properties, polyphenylene sulfide resins have drawn a good deal of attention as materials for preparing electrical and electronic parts, automotive parts and the like.
Further the resins are moldable or shapable into various articles such as parts, films, fibers, etc. by means of, for example, injection molding and extrusion molding techniques and have been employed in a variety of fields where their heat resistance and chemical resistance properties are desired or favored.
2. Prior Art
One of the typical processes for producing polyphenylene sulfide resins is disclosed in Japanese Patent Publication (KOKOKU) SHO 45-3368, which comprises reacting a dihalo-aromatic compound with an alkali metal sulfide, such as sodium sulfide, in an organic amide solvent, such as N-methyl-2-pyrrolidone. However, the product polyphenylene sulfide resins as prepared by this type of processes have such a low level of molecular weights that the resins as prepared are not directly employable in molding and shaping applications, such as injection molding. Therefore, the low molecular weight polymers have had to be modified to increase their molecular weights prior to their use in molding or shaping applications. Such modification can be effected, for example, by heating a low molecular weight material in air so as to crosslink the molecules and thereby to increase the molecular weight. However, the polymers increased in the molecular weight by this technique generally exhibit poor toughness properties.
As another approach, there have been proposed processes in which polyphenylene sulfide resins of increased molecular weights are directly prepared by polymerization reaction. Typical examples of the processes include a process in which the polyphenylene sulfide synthesis polymerization is effected in the presence of a polymerization assistant agent RCOOM, where R is a hydrocarbyl group and M is an alkali metal, as described in Japanese Patent Publication (KOKOKU) SHO 52-12240, and a process in which the polyphenylene sulfide synthesis polymerization is carried out in the presence of a specified proportion of water, as disclosed in Japanese Patent Public Disclosure (KOKAI) SHO 61-7332.
The processes based on these synthetic techniques appear to give polyphenylene sulfide resins having molecular weights higher than those achieved by the above-mentioned process of Japanese Patent Publication (KOKOKU) SHO 45-3368. The processes, however, have failed to render the product resins satisfactorily tough. Furthermore the processes can be put in practice only with a very low level of productivities.